The industry recommended way of calculating 70% of what you are capable of lifting is by first finding out the max weight you are capable of lifting for 1 repetition with each of the exercises and then taking 70% of that to perform sets of 10 to 12 reps.
This can be a very dangerous process with many of the exercises, so instead I am going to give you an effective, an accurate, and a more safe way to calculate the weight you should use during your gym workout sessions:
Please see Champion Challenge Guidelines for step-by-step instructions on how to compete and win!